Greek riot police in Athens during a protest against new austerity measures. Photograph: Panagiotis Tzamaros/AFP/Getty Images

Greece's politicians are to vote on intensely unpopular new measures needed to secure continued payment from an international bailout fund as the country remains paralysed by a two-day general strike.

Protesters headed to Syntagma Square outside the Greek parliament in Athens, while one Communist-backed union vowed to encircle parliament in an attempt to prevent politicians from accessing the building for the vote on the spending cuts and tax hikes required by Greece's international creditors.

The bill won initial approval in a vote Wednesday night, and deputies are now to vote on the details, which include the suspension on reduced pay of 30,000 public servants and the suspension of collective labour contracts.

Creditors have demanded the measures before they give Greece more funds from a €110bn package of bailout loans from other eurozone countries and the International Monetary Fund. Greece says it will run out of money in mid-November without the next €8bn instalment.

Coming after repeated rounds of belt-tightening as the government struggles to pull the country out of its debt crisis, the measures have been deeply unpopular. Even deputies from the governing Socialist party have expressed outrage, with several indicating they could vote against some of the more contentious articles in the bill. Dissent could further weaken the slim majority of the prime minister, George Papandreou. He holds 154 of the legislature's 300 seats.

Thursday's protests come a day after a demonstration by more than 100,000 people degenerated into violence, with groups of black-clad demonstrators pelting riot police with chunks of marble, paint and gasoline bombs. Police responded with volleys of teargas and stun grenades that reverberated across the Greek capital's main square.

The clashes continued sporadically into the night in the back streets near Syntagma, where protesters set fire to piles of rubbish festering on the streets after a strike by municipal workers.

Authorities said 50 police and at least three protesters were injured in the clashes.

The second day of the general strike, on Thursday, was disrupting public transport and left ships docked at port, schools and customs offices closed and state hospitals running on emergency staff. All public services were shut, while lawyers and prison guards were among those staying away from work.